Hot gas engines are generally heated by fossil fuel burned with air. For example, the combustion air mass flow may be supplied in dependence in the temperature of the heater head of the engine and the fuel mass flow may be governed in proportion to the supplied mass flow of air. Such control system will cause a constant temperature of the working gas in the high temperature variable volume chambers of the engine. The U.S. Pat. No. 3,859,794 shows an engine provided with such system.
A closed-cycle hot gas engine is very suitable for being solar heated as the working cycle is completely independent of the kind of heat source used. However, it is essential that the working gas temperature is governed so as to provide maximum efficiency of the engine in order to generate maximum power at a specific solar plant.